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Eastern Black Walnut vs Tree of Heaven

These trees are sometimes confused due to a similar shape to their compound leaves, and propensity to grow in sunny, disturbed habitats around human habitation, but they are easily distinguished if you know what to look for.

Eastern Black Walnut (Juglans nigra)

Tree of Heaven (Ailanthus altissima)

A widespread and common tree native to eastern North America, valued for its nuts as well as its wood.
A fast-growing tree, native to east Asia, and widely introduced across North America. Common in anthropogenic habitats in much of its introduced range, less common in natural areas.
Leaflets have fine, regularly-spaced serrations around their entire margins. Serrations are sometimes so fine that you need to look closely to see them.
Leaflets have one to a few coarse teeth at the base, but the rest of the leaves have smooth margins.
Bark of mature trees rugged and coarse, with deep vertical ridges and furrows.
Bark of mature trees much smoother and thinner.
Large, almost spherical nuts contained in rough, green hulls. Painful if nuts fall from the tree onto your head.
Clusters of small seeds enclosed in thin wings to aid in wind-dispersal. Not painful if seeds fall from the tree onto your head.
Branches often extend more horizontally from trunk. Even small branches often make fairly wide angles.
Most branches angle strongly upward. Branching angles are often very small.
Leaves usually have 15-19 leaflets, rarely as few as 9 or as many as 23.
Leaves usually have 11-41 leaflets. Relatively common for leaves to have 25 or more leaflets.
Foliage mildly aromatic when crushed, an aroma that can be described as citrusy, spicy, and pleasant. Nut hulls strongly aromatic.
Foliage has a strong aroma when crushed, often described as nutty but unpleasant.